The present invention relates generally to x-ray imaging systems and, more particularly, to an explosion bonded anode stem of an x-ray tube assembly.
Generally, an x-ray system such as those used for medical imaging, include a cylindrical vacuum enclosure housing a pair of opposed electrodes. One of the electrodes includes a cathode assembly which is located opposite the other electrode having a rotating disc-shaped anode assembly therein. Voltage is applied across the cathode and anode assemblies thereby causing thermal electrons emitted by the cathode to be accelerated toward the anode at a high velocity. A small portion of the energy is converted to high energy electromagnetic radiation in the x-ray spectrum with the remainder of the energy being converted to heat. These x-rays are emitted from the cylindrical enclosure and directed toward a subject for examination. The x-rays pass through the subject and are then detected by a detector assembly for subsequent image reconstruction. Application of these known x-ray systems is well known and include medical diagnostic imaging as well as security applications.
As indicated previously, only a small portion of the energy input is converted to x-rays. An overwhelming amount of the energy input is converted to heat. Typically, temperatures within the anode assembly during operation can reach upwards of 2000xc2x0 Celsius. As a result, the anode assembly and, more particularly, the bonding joints of the anode stem of the anode assembly must be resistive to thermally induced fracture as well as provide a reliable hermetic seal.
Generally, an anode stem comprises a cylindrical sleeve portion fabricated from a copper-based alloy and a pair of rings, each ring being welded or brazed to each end of the cylindrical sleeve. Typically, the rings are fabricated from a stainless steel alloy. For proper and compliant operation of an x-ray system, it is imperative that the bonding of the rings to the cylindrical sleeve are resistant to corrosion and mechanical failure. Failure of the bonds joining the sleeve and the rings jeopardizes not only proper operation of the x-ray system, but can also result in premature failure.
Commonly, brazing and/or welding is used to conjoin the rings to the sleeve. Brazing and/or welding has a number of drawbacks including increasing the inefficiency of the x-ray system. That is, brazing and/or welding requires the introduction of a third metal to the anode stem configuration. Introduction of the brazing and/or welding materials not only decreases the reliability of the hermetic seal and the resistance to mechanical and/or thermal fracture, but also introduces temperature-induced phases to the anode stem that were not previously present. Furthermore, brazing and/or welding material potentially lowers the heat transfer capabilities within the stem assembly.
Explosion-bonding or explosive cladding is well-known in the art and is a metal-working technique commonly used to join dissimilar metals into a high quality joint. Joints formed by explosion-bonding have high mechanical strength, are ultra-high vacuum tight, and can withstand drastic thermal differentiations. Explosion-bonding is a solid state process that creates an atomic bond between dissimilar metals by using the force generated by controlled detonations to accelerate one metal onto another. Explosion-bonding is also desirable because metals may be joined together without losing their pre-bonded characteristics.
Therefore, it would be desirable to design an anode stem with improved resistance to mechanical and/or thermally induced fracture and increased heat transfer capability. It would also be desirable to provide an anode stem with increased reliability of hermetic seals/and improved resistance to corrosion without introducing temperature-induced phases not previously present in the original anode stem components.
The present invention is directed to an apparatus providing explosion bonds between components of an anode stem assembly overcoming the aforementioned drawbacks. Explosion bonding the components of an anode stem assembly to one another provides a hermetic seal with increased reliability as well as providing improved mechanical strength in the anode stem joints. Furthermore, joining dissimilar metals of an anode stem assembly by implementing explosion bonding increases the heat transfer capability of the anode stem and further provides an anode stem with improved resistance to mechanical and/or thermally induced fracture. Additionally, providing an explosion bonded joint generates a simple joint micro-structure absent voids or temperature-induced phases not previously present in the anode stem materials. Also, explosion bonding the components of an anode stem assembly decreases scrap and x-ray tube loss in fabrication and yields an x-ray system with increased efficiency, longevity, and safety.
Therefore, in accordance with an aspect of the present invention, an anode stem for an x-ray tube assembly is provided. The stem includes a cylindrical sleeve having an outer surface and an inner surface wherein the sleeve further includes at least one sleeve end. A ring is also provided extending outwardly from the at least one sleeve end. The anode stem has an explosion-bonded joint connecting the ring to the at least one sleeve end.
In accordance with another aspect of the present invention, an x-ray system comprises a central enclosure including a cooling chamber housing an x-ray generator and a cooling pump configured to circulate a coolant through the x-ray system. The system further includes a cathode end positioned at one end of the central enclosure and an anode end positioned at another end of the central enclosure. The anode end has an anode stem having a cylindrical sleeve including a first and second end. A core is provided within the anode stem extending from the first end of the sleeve toward the second end of the sleeve. A threaded frustoconical bore is positioned within the core wherein the bore includes an orifice coplanar with an outer surface of the core. A first outer ring is provided and extends outwardly from the first end of the cylindrical sleeve and a second outer ring is provided extending outwardly from the second end of the cylindrical sleeve. The first outer ring is connected to the first end of the sleeve with an explosion-bonded joint and the second ring is connected to the second end of the sleeve also with an explosion-bonded joint.
In accordance with yet another aspect of the present invention, an anode stem for an x-ray tube assembly includes a cylindrical sleeve. The sleeve includes an outer surface, an inner surface, and at least one sleeve end. The anode stem further includes a ring extending outwardly from the at least one sleeve end. Also, the anode stem includes a means for joining the ring to the at least one sleeve end without an intermediary material.
Various other features, objects and advantages of the present invention will be made apparent from the following detailed description and the drawings.